A method for reducing secondary oxidation of molten steel

Abstract

The present invention provides a method for reducing secondary oxidation of molten steel, belonging to the field of metallurgical technology, and the method comprises: reducing the RH vacuum degree to a set vacuum degree within a set time period from the end of RH refining, so as to reduce the height of the molten steel in the vacuum chamber to a set height, and reducing the riser circulating gas flow rate to a first set circulating gas flow rate; adding non-oxidizing pre-melted slag in the vacuum chamber, and then performing air breaking treatment. The method prevents the molten steel liquid surface from contacting with the air due to the RH end operation by adding low-melting-point non-oxidizing pre-melted slag in the vacuum chamber under the low vacuum degree before RH air breaking and "zero circulation" of the molten steel, thereby effectively reducing the secondary oxidation of the molten steel and having good promotion value.

Description

Technical Field

[0001] The present application relates to the field of metallurgical technology, and in particular to a method for reducing secondary oxidation of molten steel. Background Art

[0002] With the gradual upgrading of steel products, customers' requirements are getting higher and higher. Cleanliness control of steel products is becoming more and more important. An important factor affecting the cleanliness of molten steel is the secondary oxidation of molten steel. Secondary oxidation mainly refers to the phenomenon that alloy elements in molten steel react with oxygen in the air, slag, and oxides in refractory materials to form new oxide phases and pollute molten steel. The inclusion of secondary oxides in molten steel is harmful and will cause a series of quality problems in the ingot.

[0003] Many steel companies have carried out various work on controlling the secondary oxidation of molten steel, such as converter endpoint oxidation control, converter slag reduction, ladle slag removal, ladle top slag modification, full protection casting of casting machine, etc. However, for molten steel produced by RH method, the existing methods cannot stably and effectively avoid the secondary oxidation of molten steel in the ladle after RH treatment. Summary of the invention

[0004] The embodiments of the present application provide a method for reducing the secondary oxidation of molten steel to solve the problem that the existing method for controlling the secondary oxidation of molten steel cannot stably and effectively avoid the secondary oxidation of molten steel in the ladle after RH treatment.

[0005] In a first aspect, an embodiment of the present application provides a method for reducing secondary oxidation of molten steel, which is applicable to molten steel after RH refining, and the method comprises:

[0006] Within a set time period from the end of RH refining, the RH vacuum degree is reduced to a set vacuum degree, so as to reduce the height of the molten steel in the vacuum chamber to a set height, and

[0007] reducing the riser circulating gas flow rate to a first set circulating gas flow rate;

[0008] Non-oxidizing pre-melted slag is added into the vacuum chamber and then the vacuum is broken.

[0009] Furthermore, the set vacuum degree is 0.7-0.8 atm.

[0010] Furthermore, the set height is 50-100 mm.

[0011] Furthermore, the first set circulating gas flow rate is 240-300 L / min.

[0012] Further, reducing the riser circulating gas flow rate to a first set circulating gas flow rate includes:

[0013] The ascending pipe circulating gas flow rate is reduced to a first set circulating gas flow rate, and the descending pipe circulating gas is opened to control the descending pipe circulating gas flow rate to a second set circulating gas flow rate.

[0014] Furthermore, the first set circulating gas flow rate is 500-600 L / min, and the second set circulating gas flow rate is 300-400 L / min.

[0015] Furthermore, the oxidation-free pre-melted slag includes the following components in mass percentage: CaO: 55-60%, Al2O3: 37-40%, SiO2≤1.5%, TiO2≤0.05%, MgO≤5%, Fe2O3≤1%, F≤0.5%, and C≤0.2%.

[0016] Furthermore, the oxidation-free pre-melted slag includes the following components in mass percentage: CaO: 58.8%, Al2O3: 39.7%, SiO2≤0.7%, TiO2≤0.03%, MgO≤1%, Fe2O3≤0.05%, F≤0.5%, and C≤0.07%.

[0017] Furthermore, the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, wherein the mass proportion of the non-oxidized pre-melted slag with a particle size of 5 to 20 mm is greater than 90%.

[0018] Furthermore, the amount of the non-oxidized pre-melted slag added is determined according to the oxidizability of the ladle top slag, including:

[0019] If the mass fraction of TFe in the ladle top slag is ≤8%, the amount of the non-oxidizing pre-molten slag added is 0.3-1 Kg / t·molten steel.

[0020] The above technical solution provided by the embodiment of the present application has the following advantages compared with the prior art:

[0021] The method for reducing secondary oxidation of molten steel provided in the embodiment of the present application reduces secondary oxidation of molten steel by controlling the RH vacuum degree before the end of RH refining; changing the argon flow rate according to different smelting stages; and developing non-oxidizing pre-melted slag. The method can stably and effectively avoid secondary oxidation of molten steel in the ladle after RH treatment, and has great promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the invention and, together with the description, serve to explain the principles of the invention.

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0024] Figure 1 A schematic flow chart of a method for reducing secondary oxidation of molten steel provided in an embodiment of the present application. DETAILED DESCRIPTION

[0025] In order to make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0026] With the gradual upgrading of steel products, customers' requirements are getting higher and higher. Cleanliness control of steel products is becoming more and more important. An important factor affecting the cleanliness of molten steel is the secondary oxidation of molten steel. Secondary oxidation mainly refers to the phenomenon that alloy elements in molten steel react with oxygen in the air, slag, and oxides in refractory materials to form new oxide phases and pollute molten steel. The inclusion of secondary oxides in molten steel is harmful and will cause a series of quality problems in the ingot.

[0027] Many steel companies have carried out various work on controlling the secondary oxidation of molten steel, such as converter endpoint oxidation control, converter slag reduction, ladle slag removal, ladle top slag modification, full protection casting of casting machine, etc. However, for molten steel produced by RH method, the existing methods cannot stably and effectively avoid the secondary oxidation of molten steel in the ladle after RH treatment.

[0028] In view of this, the present application provides a method for reducing the secondary oxidation of molten steel, which can effectively solve the above-mentioned problems existing in the existing methods for reducing the secondary oxidation of molten steel.

[0029] The technical solution provided by the embodiment of the present invention is to solve the above technical problems, and the overall idea is as follows:

[0030] In a first aspect, an embodiment of the present application provides a method for reducing secondary oxidation of molten steel, which is applicable to molten steel after RH refining, and the method comprises:

[0031] Within a set time period from the end of RH refining, the RH vacuum degree is reduced to a set vacuum degree, so as to reduce the height of the molten steel in the vacuum chamber to a set height, and

[0032] reducing the riser circulating gas flow rate to a first set circulating gas flow rate;

[0033] Non-oxidizing pre-melted slag is added into the vacuum chamber and then the vacuum is broken.

[0034] The method for reducing secondary oxidation of molten steel provided in the embodiment of the present application reduces secondary oxidation of molten steel by controlling the RH vacuum degree before the end of RH refining; changing the argon flow rate according to different smelting stages; and developing non-oxidizing pre-melted slag. The method can stably and effectively avoid secondary oxidation of molten steel in the ladle after RH treatment, and has great promotion value.

[0035] Secondary oxidation is the oxidation that occurs in molten steel during tapping, transportation, casting, etc. after the deoxidation and refining processes are completed. It is mainly a process in which the completely deoxidized molten steel absorbs oxygen from the air, oxidizing slag or refractory materials, resulting in an increase in the total oxygen content in the steel. Therefore, the mass transfer process of reactive elements at the interface is very important, and interfacial reaction is often the limiting link.

[0036] As an implementation method of the present invention, the set vacuum degree is 0.7-0.8 atm.

[0037] Before the end of RH refining treatment, it is necessary to ensure extremely high vacuum (the numerical value shows 0mbar), and the height of molten steel submerged in the vacuum chamber is ≥350mm, generally 350-550mm, to ensure that the molten steel is fully degassed, fully mixed, and inclusions are removed. Reducing the vacuum degree in a short time before the end of the treatment has little effect on the degassing of the molten steel, and at the same time, low vacuum can reduce the circulation rate of the molten steel and the height of the molten steel in the vacuum chamber, so that the added non-oxidizing non-oxidizing pre-melted slag has as little contact with the molten steel as possible (because even the "non-oxidizing" non-oxidizing pre-melted slag has a certain oxygen content).

[0038] As an implementation manner of the embodiment of the present invention, the set height is 50-100 mm.

[0039] By controlling the height of the molten steel in the vacuum chamber, the non-oxidized pre-melted slag can be kept in contact with the molten steel as little as possible.

[0040] As an implementation method of the embodiment of the present invention, the first set circulating gas flow rate is 240-300 L / min

[0041] The circulation velocity of the molten steel is reduced by reducing the circulation gas flow rate, thereby reducing the stirring energy of the molten steel, so that the added non-oxidized non-oxidized pre-melted slag has less contact with the molten steel.

[0042] As an implementation manner of an embodiment of the present invention, reducing the riser circulating gas flow rate to a first set circulating gas flow rate includes:

[0043] The ascending pipe circulating gas flow rate is reduced to a first set circulating gas flow rate, and the descending pipe circulating gas is opened to control the descending pipe circulating gas flow rate to a second set circulating gas flow rate.

[0044] By controlling the circulating gas flow rate of the riser and the circulating gas flow rate of the tube, the circulating flow rate of the molten steel is reduced, thereby reducing the contact between the added non-oxidized pre-molten slag and the molten steel.

[0045] As an implementation manner of the embodiment of the present invention, the first set circulating gas flow rate is 500-600 L / min, and the second set circulating gas flow rate is 300-400 L / min.

[0046] As an implementation mode of an embodiment of the present invention, the oxidation-free pre-melted slag includes the following components in mass percentage: CaO: 55-60%, Al2O3: 37-40%, SiO2≤1.5%, TiO2≤0.05%, MgO≤5%, Fe2O3≤1%, F≤0.5%, and C≤0.2%.

[0047] This non-oxidizing pre-melted slag can be melted quickly and has extremely low oxidizing properties, which reduces the secondary oxidation of deoxidized molten steel. At the same time, due to the molten steel produced by the RH method, the RH immersion tube occupies a certain space on the top of the slag and molten steel in the ladle, resulting in the molten steel being exposed at the end of the treatment, which is not conducive to controlling the oxidation of the molten steel. Before the end of the RH treatment, non-oxidizing pre-melted slag is added to the vacuum chamber, so that the non-oxidizing pre-melted slag can fall into the exposed part of the molten steel as the molten steel circulates, reducing the secondary oxidation of the molten steel during the RH end-casting process of the casting machine.

[0048] As an implementation mode of an embodiment of the present invention, the oxidation-free pre-melted slag includes the following components in mass percentage: CaO: 58.8%, Al2O3: 39.7%, SiO2≤0.7%, TiO2≤0.03%, MgO≤1%, Fe2O3≤0.05%, F≤0.5%, and C≤0.07%.

[0049] As an implementation method of an embodiment of the present invention, the amount of non-oxidized pre-melted slag added is determined according to the oxidizability of the ladle top slag, including:

[0050] If the mass fraction of TFe in the ladle top slag is ≤8%, the amount of the non-oxidizing pre-molten slag added is 0.3-1 Kg / t·molten steel.

[0051] The relationship between the amount of non-oxidizing pre-melted slag added and the oxidizability of the ladle top slag is shown in Table 1 below.

[0052] Table 1 Relationship between the amount of non-oxidizing pre-melted slag added and the oxidizability of the ladle top slag

[0053]

[0054] By controlling the mass percentage of TFe in the ladle top slag to be below 8%, the oxidizability of the ladle top slag can be controlled, so that the amount of non-oxidizing pre-melted slag added can be determined to prevent secondary oxidation of molten steel.

[0055] According to tests, the method of the present invention can effectively reduce the secondary oxidation of molten steel, and the T[O] of molten steel in the tundish can be reduced by 20%.

[0056] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only intended to illustrate the present invention and are not intended to limit the scope of the present invention. The experimental methods in the following examples that do not specify specific conditions are usually measured according to national standards. If there is no corresponding national standard, then proceed according to general international standards, conventional conditions, or according to the conditions recommended by the manufacturer.

[0057] Example 1

[0058] This embodiment provides a method for reducing secondary oxidation of molten steel, and its flow chart is as follows: Figure 1 As shown, specifically:

[0059] (1) 2 minutes before the end of the RH refining treatment, the RH vacuum degree was reduced to 0.7 atm, so that the height of the molten steel in the vacuum chamber was 75 mm;

[0060] (2) 2 minutes after the RH refining treatment, the riser circulating gas flow rate was reduced to 270 L / min;

[0061] (3) When the RH vacuum degree and circulating gas flow rate are reduced to the target value, 0.8 kg / t of non-oxidized pre-melted slag (the mass percentage of TFe in the ladle top slag is 6%) is added into the vacuum chamber, and then the vacuum is broken after waiting for 30 seconds;

[0062] Among them, the non-oxidized pre-melted slag includes the following components in mass percentage: CaO: 58.8%, Al2O3: 39.7%, SiO2: 0.5%, TiO2: 0.03%, MgO: 0.5%, Fe2O3: 0.05%, F: 0.3%, C: 0.07%; the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, of which the non-oxidized pre-melted slag with a particle size of 5 to 20 mm accounts for 95%.

[0063] Example 2

[0064] This embodiment provides a method for reducing secondary oxidation of molten steel, specifically:

[0065] (1) 1 minute before the end of the RH refining treatment, the RH vacuum degree was reduced to 0.8 atm, so that the height of the molten steel in the vacuum chamber was 75 mm;

[0066] (2) 1 minute after the RH refining treatment ends, the riser circulating gas flow rate is reduced to 240 L / min;

[0067] (3) When the RH vacuum degree and circulating gas flow rate are reduced to the target value, add 0.6 kg / t of non-oxidized pre-melted slag (the mass percentage of TFe in the ladle top slag is 4%) into the vacuum chamber, and then wait for 30 seconds before breaking the vacuum;

[0068] Among them, the non-oxidized pre-melted slag includes the following components in percentage by mass: CaO: 55%, Al2O3: 40%, SiO2: 1%, TiO2: 0.05%, MgO: 2%, Fe2O3: 1%, F: 0.5%, C: 0.2%; the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, of which the non-oxidized pre-melted slag with a particle size of 5 to 20 mm accounts for 92%.

[0069] Example 3

[0070] This embodiment provides a method for reducing secondary oxidation of molten steel, specifically:

[0071] (1) 1.5 minutes before the end of the RH refining treatment, the RH vacuum degree was reduced to 0.8 atm, so that the height of the molten steel in the vacuum chamber was 75 mm;

[0072] (2) 1.5 minutes after the RH refining treatment, the riser circulating gas flow rate was reduced to 300 L / min;

[0073] (3) When the RH vacuum degree and circulating gas flow rate are reduced to the target value, 0.4 kg / t of non-oxidized pre-melted slag (the mass percentage of TFe in the ladle top slag is 2%) is added into the vacuum chamber, and then the vacuum is broken after waiting for 30 seconds;

[0074] Among them, the non-oxidized pre-melted slag includes the following components in percentage by mass: CaO: 60%, Al2O3: 37%, SiO2: 1.5%, TiO2: 0.02%, MgO: 0.6%, Fe2O3: 0.2%, F: 0.4%, C: 0.1%; the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, of which the non-oxidized pre-melted slag with a particle size of 5 to 20 mm accounts for 94%.

[0075] Example 4

[0076] This embodiment provides a method for reducing secondary oxidation of molten steel, specifically:

[0077] (1) 2 minutes before the end of the RH refining treatment, the RH vacuum degree was reduced to 0.7 atm, so that the height of the molten steel in the vacuum chamber was 75 mm;

[0078] (2) 2 minutes after the RH refining treatment is completed, the circulating gas flow rate of the ascending pipe is reduced to 550 L / min, and the circulating gas of the downcomer is opened at the same time, and the circulating gas flow rate of the downcomer is controlled at 350 L / min;

[0079] (3) When the RH vacuum degree and circulating gas flow rate are reduced to the target value, add 0.5 kg / t of non-oxidized pre-melted slag (the mass percentage of TFe in the ladle top slag is 3%) into the vacuum chamber, and then wait for 30 seconds before breaking the vacuum;

[0080] Among them, the non-oxidized pre-melted slag includes the following components in percentage by mass: CaO: 57%, Al2O3: 38%, SiO2: 1.2%, TiO2: 0.04%, MgO: 2%, Fe2O3: 0.05%, F: 0.3%, C: 0.03%; the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, of which the non-oxidized pre-melted slag with a particle size of 5 to 20 mm accounts for 93%.

[0081] Example 5

[0082] This embodiment provides a method for reducing secondary oxidation of molten steel, specifically:

[0083] (1) 2 minutes before the end of the RH refining treatment, the RH vacuum degree was reduced to 0.7 atm, so that the height of the molten steel in the vacuum chamber was 75 mm;

[0084] (2) 2 minutes after the RH refining treatment is completed, the circulating gas flow rate of the ascending pipe is reduced to 600 L / min, and the circulating gas of the downcomer is opened at the same time, and the circulating gas flow rate of the downcomer is controlled at 400 L / min;

[0085] (3) When the RH vacuum degree and circulating gas flow rate are reduced to the target value, add 0.5 kg / t of non-oxidized pre-melted slag (the mass percentage of TFe in the ladle top slag is 3%) into the vacuum chamber, and then wait for 30 seconds before breaking the vacuum;

[0086] Among them, the non-oxidized pre-melted slag includes the following components in percentage by mass: CaO: 57%, Al2O3: 38%, SiO2: 1.2%, TiO2: 0.04%, MgO: 2%, Fe2O3: 0.05%, F: 0.3%, C: 0.03%; the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, of which the non-oxidized pre-melted slag with a particle size of 5 to 20 mm accounts for 93%.

[0087] Example 6

[0088] This embodiment provides a method for reducing secondary oxidation of molten steel, specifically:

[0089] 2 minutes before the end of RH refining treatment, the RH vacuum degree was reduced to 0.7 atm, so that the height of molten steel in the vacuum chamber was 75 mm;

[0090] 2 minutes after the RH refining treatment is completed, the circulating gas flow rate of the ascending pipe is reduced to 500 L / min, and the circulating gas of the downcomer is opened at the same time, and the circulating gas flow rate of the downcomer is controlled at 300 L / min;

[0091] When the RH vacuum degree and circulating gas flow rate are reduced to the target value, add 0.5 kg / t of non-oxidized pre-melted slag (the mass percentage of TFe in the ladle top slag is 3%) into the vacuum chamber, and then wait for 30 seconds before breaking the vacuum;

[0092] Among them, the non-oxidized pre-melted slag includes the following components in percentage by mass: CaO: 57%, Al2O3: 38%, SiO2: 1.2%, TiO2: 0.04%, MgO: 2%, Fe2O3: 0.05%, F: 0.3%, C: 0.03%; the particle size of the non-oxidized pre-melted slag is 5 to 30 mm, of which the non-oxidized pre-melted slag with a particle size of 5 to 20 mm accounts for 93%.

[0093] In summary, the method for reducing the secondary oxidation of molten steel provided by the present invention can stably and effectively avoid the secondary oxidation of molten steel in the ladle after RH treatment; this method prevents the RH ending operation from causing the molten steel surface to contact with the air by adding low-melting-point non-oxidizing pre-molten slag in the vacuum chamber under low vacuum before RH breaking and "zero circulation" of molten steel, thereby effectively reducing the secondary oxidation of molten steel and having good promotion value.

[0094] It should be noted that, in this article, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise a ..." do not exclude the existence of other identical elements in the process, method, article or device including the elements.

[0095] The foregoing is merely a specific embodiment of the present invention, which enables those skilled in the art to understand or implement the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for reducing secondary oxidation of molten steel, characterized in that: Applicable to molten steel after RH refining, the method comprises: Within a set time period from the end of RH refining, the RH vacuum degree is reduced to a set vacuum degree, so as to reduce the height of the molten steel in the vacuum chamber to a set height, and reducing the riser circulating gas flow rate to a first set circulating gas flow rate; Add non-oxidized pre-melted slag into the vacuum chamber and then perform vacuum breaking treatment; The setting time is ≤ 2 min, the setting vacuum degree is 0.7-0.8 atm, the setting height is 50-100 mm, and the lowering of the rising tube circulating gas flow rate to the first setting circulating gas flow rate includes: Reduce the rising pipe circulating gas flow rate to a first set circulating gas flow rate, and open the downcomer circulating gas, and control the downcomer circulating gas flow rate to a second set circulating gas flow rate, wherein the first set circulating gas flow rate is 500-600 L / min, and the second set circulating gas flow rate is 300-400 L / min; The non-oxidized pre-melted slag includes the following components in mass percentage: CaO: 55-60%, Al2O3: 37-40%, SiO2≤1.5%, TiO2≤0.05%, MgO≤5%, Fe2O3≤1%, F≤0.5%, and C≤0.2%.

2. The method for reducing secondary oxidation of molten steel according to claim 1, characterized in that: The non-oxidized pre-molten slag includes the following components in mass percentage: CaO: 58.8%, Al2O3: 39.7%, SiO2≤0.7%, TiO2≤0.03%, MgO≤1%, Fe2O3≤0.05%, F≤0.5%, and C≤0.07%.

3. The method for reducing secondary oxidation of molten steel according to claim 2, characterized in that: The particle size of the non-oxidized pre-melted slag is 5-30 mm, wherein the mass proportion of the non-oxidized pre-melted slag with a particle size of 5-20 mm is greater than 90%.

4. The method for reducing secondary oxidation of molten steel according to claim 3, characterized in that: If the mass fraction of TFe in the ladle top slag is ≤8%, the amount of the non-oxidizing pre-melted slag added is 0.3-1 kg / t·molten steel.

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